The geomagnetic dipole moment variation between 250 and 800 ka BP reconstructed from the authigenic 10Be/9Be signature in West Equatorial Pacific sediments

The authigenic 10Be/9Be ratio, proxy of the cosmogenic radionuclide 10Be production rate in the atmosphere, was measured in sediments deposited in the West Equatorial Pacific (Gulf of Papua; 10°25 S; 146°15 E), in order to reconstruct the geomagnetic dipole moment variations in the 250–800 ka time interval, independently from paleomagnetic methods. The pelagic clayey-carbonate muds continuously deposited between marine isotope stages 8 and 20 were subsampled every 10 cm. The 10Be production rate record reconstructed for the 250–800 ka interval is described and compared over the same time interval with global paleomagnetic stacks (SINT-2000 and PISO-1500). The highlighted cosmogenic 10Be overproductions appear to be triggered by the series of Geomagnetic Dipole Lows (GDL) that have occurred since the Brunhes–Matuyama reversal. Calibration using absolute values of the geomagnetic dipole moment drawn from a paleomagnetic database produces a new record of the dipole moment variations over the 250–800 ka time interval. The timing and amplitude of the GDL succession revealed by such records will contribute to improving knowledge of the geodynamo rhythms and rate of changes at millennial to million year scales.